Resonant cavity magnetrons



APll 15, 1958 w. E. wlLLsHAw 2,831,148

REsoNANT CAvITY MAGNETRoNs Filed Aug. 18, 1953 ilnited States Patent O REsoNANT cAvrrY MAGNETRoNs William Ernest Willshaw, Kenton, England, assignor to The M-O Valve Company Limited, London, England Application August 18, 1953, Serial No. 375,040

Claims priority, application Great Britain August 19, 1952 6 Claims. (Cl. S15-39.53)

This invention relates to magnetrons of the type comprising within a sealed evacuated envelope a metal block anode pierced by a cylindrical hole within which is supported the cathode of the magnetron, and from the surface of which hole are recessed into the block a plurality of cavity resonators which are evenly spaced round the cathode. Usually the metal block is formed integral with a metal part of the sealed envelope to which the anode connection (usually earth) is arranged to be made, and leads to the cathode, and also to the cathode heater which is usually provided, are sealed through the envelope. In addition output coupling means for coupling the magnetron to a load circuit are also provided, and this invention is particularly concerned with the form of the output coupling means.

Hitherto the output coupling means has usually consisted of a lead terminating in a coupling loop within one of the anode cavities or connected to one of the anode segments formed between the cavities, the lead either passing to the exterior of the sealed envelope or being arranged for the radiation of energy through a part of the envelope, for example for the excitation of a waveguide fitted over said part, which waveguide forms part of the load circuit.

The object of the invention is to provide an improved form of coupling means of this kind.

According to the invention in a magnetron of the type specified the output coupling means comprises two conducting leads which are connected to the anode system so as to be driven in anti-phase in normal operation of the magnetron and are connected to each other at their ends away from the anode system so as to form a loop from which -output energy from the magnetron is arranged to be obtained.

Preferably the effective electrical length of the combined leads is equal to one half wavelength, or odd integral multiple thereof, at the normal operating frequency of the magnetron.

Preferably the said two conducting leads are integral with each other and are formed by bending a single length of wire into substantially U-shape, the limbs of the U forming part of the said leads and being connected at their ends to the anode system, and the bend of the U forming an output loop.

For driving in anti-phase, the conducting leads may be connected to points on the anode system the high frequency potential at which oscillate in anti-phase in normal operation of the magnetron, but in the case where the conducting leads terminate in coupling loops, these may if desired be located in cavity resonators the electrical fields within which are in phase in normal operation, and the required anti-phase operation may then be obtained by opposite orientation of the coupling loops.

Preferably with a magnetron adapted for operation in the 1rmode, the conducting leads terminate in oppositely oriented coupling loops located in resonators which are separated by one intervening resonator.

2,831,148 Pgented Apr. 15, s

Preferably in a magnetron in accordance with the invention, the end of the output loop lies within a glass side-tube part of the envelope over which can be fitted an external wave-guide for conveying away from the magnetron oscillations radiated from the output loop in operation of the magnetron. I

One embodiment of the invention will now be described by way of example with reference to Figures l and 2 of the accompanying drawing, of which Figure 1 shows a side view of the magnetron with one end plate removed to reveal the anode system, and Figure 2 show a plan view, looking at Figure l from above.

In this embodiment the magnetron comprises a rectangular copper block 1 recessed from each end face to leave a central portion 2 which forms the anode proper; the portion 2 is pierced by a central hole 3 within which is mounted coaxially the cathode 4 of the magnetron.

The cathode 4 is of the well known indirectly heated kind consisting of a cylindrical nickel tube coated with electron emissive material on its outer surface and containing a heater within the tube; the tube is supported between end discs which are carried by tungsten rods 5 which are sealed through the block 1 by means of copper-glass side-stents 6 of well known kind, the cathode tube being insulated from one of the rods, which rod is arranged to serve as one of the heater leads, and the other rod serving both as the other heater lead and as a lead to the cathode, in well known manner. Only one of the cathode end discs appears in the view shown in Figure l and for the sake of clarity no details of the cathode have been indicated in Figure 2.

The anode system of the magnetron comprises fourteen cavity resonators evenly spaced round the cathode 4 and each formed by the combination of a rectangular slot '7 and a circular hole 8 cut through the anode 2 parallel to its axis.

From the bottom of two of the holes 8 which are separated by one intervening hole, further holes 9 eX- tend perpendicular to the axis of the anode, and parallel to each other, to the exterior of the block; into the holes 9 are brazed copper bushings lil and along each of these bushings passes one limb of a U-shaped output loop 11, the bend of which projects into a copper-glass side-stem 12' sealed to the block' over the holes 9. The two ends of the loop 11 are formed as coupling loops lying Within the holes S and the end of the loop in each hole is brazed to the inner end of the corresponding bushing 10, the whole output loop being supported thereby. The coupling loops within the resonators are oppositely directed for driving in anti-phase and the total electrical length of the output loop (i. e. of the whole of the U) is an odd integral multiple of one half wavelength at the normal operating frequency of the magnetron.

The output arrangement for the magnetron includes also a ange 13 attached to the block 1 round the sidestem 12, this flange serving in use of the magnetron for the attachment of a waveguide (not shown) arranged to be excited by energy radiated from the loop 11.

The anode system is completed by the attachment, at each end face of the anode 2, of two concentric modespacing straps 14 and 15 of known kind set into a groove formed in the end face in the region of the anode segments between the slots 7 and attached to alternate anode segments in known manner, these straps not being indicated in Figure 2.

rl`he block 1 is closed at each end by copper side-plates 16 and 17 attached thereto by gold washer seals in known manner, one of these plates being shown removed in the Figure l view. The block l also has attached to it copper tins 18 for assisting in cooling the block in operation of the magnetron.

It has been found that a magnetron constructed in this Way is much less liable to change its mode of operation when a change of matching of the output circuit occurs than is a similar magnetron in which the output system is coupled to one anode cavity only.

I claim:`

l. A magnetron having a sealed evacuated envelope containing a metal block anode pierced by a cylindrical hole within which is supported the cathode of the magnetron, a plurality of cavity resonators recessed into the block from the surface of said hole and evenly spaced round the cathode, and output coupling means comprising two conducting leads connected to the anode system at points providing anti-phase excitation of the leads in normal operation of the magnetron, said leads being connected to each other at their ends away from the anode system to form an output coupling loop the effective electrical length of which is an odd integral multiple of a halt' wave length at the normal operating frequency of lthe magnetron.

2. A magnetron according to claim l wherein the two said leads are integral with each other and are formed by bending a single length of wire into substantially U-shape, the limbs of the U forming part of the said leads and being connected at their ends to the anode system, and the bend of the U forming an output loop.

3. A magnetron according to claim 1 wherein the said leads are similar and are connected to points ,on the anode system which oscllate in anti-phase in normal operation of the magnetron.

4. A magnetron according to claim 1 wherein the said leads terminate in coupling loops and are located in cavity resonators the electrical ields within which are in phase in normal operation of the magnetron, the coupling loops being oppositely oriented for securing the required antiphase excitation of the leads in operation o' the magnetron.

5. A magnetron according to claim 4 which is arranged for operation in the 1rmode and in which the oppositely oriented coupling loops are located in resonators which are separated by one intervening resonator.

6. A magnetron according to claim 1 wherein the end of the output loop lies within a glass side-tube part of the envelope over which can be fitted an external wave-guide for conveying away from the magnetron oscillations radiated from the output loop in operation of the magnetron.

References Citedn the file of this patent UNITED STATES PATENTS 2,348,986 Linder May 16, 1944 2,504,329 Heising Apr. 18, 1950 2,504,894 Sloan Apr. 18, 1950 2,642,551 Litton lune 16, 1953 

